Conventionally, in dialysis treatment or the like, a blood purification device has been used for purifying and circulating collected patient's blood outside a body and again returning the blood into the body. Such a blood purification device includes a fluid path through which blood or a dialysis fluid flows. The fluid path includes a blood line through which blood flows, a dialysis fluid line through which a dialysis fluid flows, a dialyzer including a hollow fiber membrane (blood purification membrane), and the like. To a distal end of the blood line, an artery side puncture needle and a vein side puncture needle are attached. The puncture needles are inserted into a patient to perform extracorporeal circulation of blood in the dialysis treatment.
Before passing blood or a dialysis fluid through the fluid path, a process called “priming” is typically performed for supplying a priming fluid that is physiological saline or a dialysis fluid into the fluid path to fill the fluid path. The priming process is performed to wash the fluid path, improve wettability, and so on. In such a priming process, in order to remove air remaining in the fluid path, a healthcare personnel taps a dialyzer or a pipe by hand so that attached air bubbles flow. However, such manual removal of air bubbles is troublesome.